One of the constants in history is the malleability of political boundaries. In America, we have become a bit inured to this fact because our own geography has been so steady, adding only Hawaii and Alaska to our country in the last century. But Europe is used to change, and nowhere in Europe has there been more change than in the Balkan area. Trieste is a city that lies at the end of the Adriatic and has had many masters during its history.
Trieste began the stamp period as part of the Austro-Hungarian empire. As such, like any city in the empire, it used Austrian stamps. After WWI, Austria ceded the area that included Trieste to Italy, and the importance of Trieste as a commercial center declined. Trieste had been an important port city for Austro-Hungary